IMPROVED FLOTATION OF FINE PGM TAILINGS WITH A HIGH SHEAR CAVITATION DEVICE N^Victor RossMineral Processing Division, Mintek, 200 Malibongwe Drive, Randburg 2125 South Africa

摘要

A significant amount of liberated fine valuable particles is lost to flotation tailings streams due to inefficient collection by air bubbles and deactivation by oxidation and slimes. Extensive research has been done in this area to improve recoveries, including the use of micro bubble generators and dissolved air flotation, the agglomeration of fines, sonication and attritioning to clean surfaces, removal of oxidation products by chemical methods, the activation of surfaces by suphidisation and changes in Eh, and the use of alternative collectors to float hydroxides and oxides.An exciting prospect is the use of high shear cavitation devices (HSCDs), in which the feed slurry is intimately contacted with air in a high pressure environment, typically a series of venturi's. This promotes cavitation and the formation of ultrafine bubbles on particle surfaces, which is believed to aid the agglomeration and recovery of fines. In addition, it is expected that successive passes of slurry through the reactor aids the cleaning of particle surfaces, and that additional liberation through attritioning may also occur as a result of the strong intra-particle action. A fourth mechanism is believed to be due to the significant increase in gas holdup in the pulp phase when compared to that in conventional cells, resulting in a different hydrodynamic environment.This paper details recent investigations that have been undertaken at Mintek on the Mach HSCD reactor, using a PGM tailings sample, to better understand these mechanisms. In this first phase of the work, the effect of preconditioning has been studied by comparing the results against that of a baseline obtained in a conventional cell. The results suggest that the dominant mechanism responsible for an improved recovery is due to the cleaning of particle surfaces, not only activating the valuable mineral surfaces but presumably also deactivating that of the gangue. Compared to the baseline, significant improvements in recovery together with a drop in mass pull were observed, resulting in final projected grade increases of 61, 45 and 65% respectively for the cyclone overflow, cleaner feed and recleaner feed respectively. PGM recoveries were increased accordingly by 23, 44 and 31% respectively. It is unclear at this stage to what extent the nucleation of micro bubbles on particle surfaces, and the resultant aggregation of these particles, is a contributing mechanism.Further testwork is underway to investigate the various mechanisms more closely, and expand the potential range of applications of this technology, particularly minimising PGM losses with interstage chrome removal from UG2 flotation circuits.